1. Field of the Invention
Minerals are extracted from the earth in a variety of ways, determined to a great extent by the physical state in which the minerals naturally occur. Petroleum is always extracted by wells drilled into the earth. In formations that have sufficient naturally occurring underground pressure, the petroleum flows to the earth's surface, but if the formation pressure is insufficient to cause the petroleum to flow to the surface, it is pumped to the surface. Natural gas is recovered by wells penetrating a gas bearing formation with the pressure of the gas causing it to flow to the earth's surface.
On the other hand, minerals that naturally occur in a solid state are more difficult to remove. Coal and most metal bearing ores are commonly removed by mines dug from the earth's surface into the producing formation. Coal or metal bearing ores are removed as solids and, after being removed from a mine, are conveyed by trucks or conveyor belts to a processing plant. Solid mineral bearing ores are also removed by surface mining, that is, by digging strip pits in which the overburden is removed and thereafter the mineral bearing ore is physically removed. Some types of ores are removed by large open pit mines dug in the form of a large crater with circumferential shelves circling the mine core by which equipment is moved into the mine and by which ore is removed from it.
In some cases, minerals that occur naturally as a solid can be removed by wells rather than removing the solid ore from the earth. This technique is called solution mining. The present invention is concerned with an improved system, and method of use thereof, for solution mining.
2. Prior Art
Ore can be extracted through wells even when the ore is not in situ a naturally occurring liquid or gas. As an example, U.S. Pat. No. 4,869,555, entitled "Apparatus for Recovery of Sulphur" discloses in detail a system for recovering sulphur from an underground formation in which a solvent, in this case hot water, is injected into the formation to produce a sulphur solution that is then conveyed to the earth's surface where the sulphur content is recovered. Others have extracted viscous petroleum from subterranean formations by heating the viscous hydrocarbon products by the injection of steam or hot water to raise the viscosity sufficient to allow the hydrocarbon products to be pumped to the earth's surface. An example of such a system for mining viscous petroleum is revealed in U.S. Pat. No. 3,951,457 entitled "Hydraulic Mining Technique for Recovering Bitumen from Tar Sand Deposit."
An additional technique for extracting minerals hydraulically is disclosed in U.S. Pat. No. 4,074,779 entitled "Backwashing System for Slurry Pick-up Used in Hydraulic Borehole Mining Devices." This patent teaches a system wherein high pressure water jets are used to cut mineral to be mined to form a slurry that is then picked up and conveyed to the earth's surface. In this system, the mined minerals remain as small size solids that are conveyed in a slurry.
These previously issued United States patents and the references cited in them form a good background for the present invention.
In addition to the patents above discussed, other prior art that provides additional background information to the subject matter of the present invention may be found in the following United States patents:
______________________________________ PATENT NO. INVENTOR ______________________________________ 3,155,177 Fly 3,278,233 Hurd et al. 3,652,129 Edmonds 3,713,698 Rhoades 3,816,027 Miscovich 3,951,457 Redford 4,035,023 Cockrell 4,074,779 Cheung et al. 4,077,671 Bunnelle 4,140,346 Barthel 4,241,953 Bradford et al. 4,302,052 Fischer 4,346,936 Yan 4,348,058 Coakley et al 4,358,157 Showalter 4,452,490 Yan 4,869,555 Peters et al. 5,685,374 Schmidt et al. ______________________________________